196 



Minnesota Plant Diseases. 



The latter derives its benefit in the nitrate product. A true part- 

 nership is thus effected. Clover and alfalfas and all such nodule- 

 possessing plants are therefore valuable rotation crops because 

 they accumulate by the aid of their bacterial partners nitrates, 

 where wheat or other crops have depleted the soil of these com- 

 pounds. These bacteria are now distributed by the Depart- 

 ment of Agriculture in quantity for sowing on poor soils where 

 leguminous plants as clovers, etc., are then grown. Such soils 

 can thus be greatly enriched so that other crops which do not 

 possess bacterial nodules can subsequently be raised. 



Other economic phases 



Fig. 99. — The bacteria of such root nodules of 

 the pea family as are shown in Fig. 98. 

 On the left of Vicia sativa (the .spring 

 vetch), on the right of Medicago denti- 

 culata. Very highly magnified. After At- 

 kinson. 



of bacteria. A great many 

 other phases of bacterial life 

 are of importance in the 

 arts and industries and only 

 a few may be mentioned in 

 this short review. In tan- 

 ning, in diseases of wine and 

 beer, rennet curdling, in the 

 manifold processes of putri- 

 faction of organic matter, in 

 cheese industries, in the deposition of bog iron ore, the bacteria 

 appear in important roles. More particularly are we here con- 

 cerned with those forms which attack living plants and cause 

 disease. Such plant diseases are not numerous but investiga- 

 tion is steadily adding new examples and they promise to be- 

 come of sufficient importance to make this brief general dis- 

 cussion of this group of plants justifiable. The various bacte- 

 rial diseases will be considered individually in subsequent chap- 

 ters. (Figs. 96 to 99, 172 to 178, 195). 



Slime molds (Mycctosoa). This group of organisms is 

 now commonly classified with the simplest animals, though 

 they are very fungus-like in many of their characters. Most 

 slime molds are true saprophytes but a few have adopted para- 

 sitic habits. Some of the latter live in plants and others in ani- 

 mal tissues. The slime molds produce spores in structures very 

 similar to the fruiting bodies of many saprophytic fungi. These 

 fruiting bodies are usually very small — many are of pin-head 

 size but a few attain a diameter of six inches. The spores are 



